Magnetic substrate, coil component, and circuit board

Abstract

To provide a magnetic substrate excellent in an electrical insulation property.SOLUTION: A magnetic substrate contains sintered particles 1 that are formed with ferrite including Ni and Zn, and is formed with a sintered body 10a having a surface layer 2 on a surface with more than or equal to 20% of rate of a mol number of Cu2O based on a total mol number of a copper oxide.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a magnetic substrate, a coil component, and a circuit board.

Background Art

[0002] In recent years, there has been an increasing demand for miniaturization and high performance of electronic components. Among electronic components, for coil components, even when the volume of the magnetic substrate is reduced due to miniaturization, it is required to ensure low loss. Since the loss in coil components is generated by the flow of current in the magnetic substrate, improving the electrical insulation of the magnetic substrate is effective for reducing the loss of coil components. For this reason, as a material constituting the magnetic substrate, attempts have been made to enhance the electrical insulation of the magnetic substrate by using a Ni-Zn-based ferrite having excellent electrical insulation as a base and applying various improvements thereto.

[0003] For example, Patent Document 1 discloses a technical idea in which a ferrite sintered body constituting a magnetic substrate contains, in 100 mol% of the main component composition, Fe of 49 mol% or more and 50 mol% or less in terms of Fe2O3, Zn of 32 mol% or more and 34.5 mol% or less in terms of ZnO, Ni of 6.5 mol% or more and 12.5 mol% or less in terms of NiO, and Cu of 5 mol% or more and 9 mol% or less in terms of CuO, and ZnO is present at the grain boundaries of ferrite crystals composed of the main component. Further, in the same document, as a method for manufacturing the ferrite sintered body, after mixing the main components and calcining to obtain a calcined body, zinc oxide serving as a ZnO source to be present at the crystal grain boundaries is added, pulverized and mixed, and fired through granulation and molding.

[0004] Further, Patent Document 2 discloses a technical idea in which a magnetic substrate is composed of a Ni-Cu-Zn-based ferrite material that contains only TiO2 as a sub-component excluding inevitable impurities, and when the content of TiO2 is x, 0.1 wt% < x ≤ 4.0 wt%.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] International Publication No. 2013 / 015074 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-132715 Summary of the Invention [Problem to be solved by the invention]

[0006] Varying the timing of compounding raw materials as in Patent Document 1, or adding raw materials other than the constituent components of the ferrite material as in Patent Document 2, can easily result in uneven dispersion because the amount of the additional raw materials is very small compared to the main components, which can cause the magnetic substrate to fail to have the desired electrical insulation. The production of a magnetic substrate that does not have the desired electrical insulation can lead to the formation of coil components with high loss.

[0007] The present invention has been made in view of the above-mentioned problems, and has as its object to provide a magnetic substrate having excellent electrical insulation properties. [Means for solving the problem]

[0008] The present inventors have conducted various studies to achieve the above-mentioned object, and have found that the above-mentioned problems can be solved by forming a surface layer containing copper oxide, in which the copper oxide has a relatively high content of CuO, on the surface of a Ni-Zn-based ferrite sintered body, and have thus completed the present invention.

[0009] That is, one aspect of the present invention for solving the above-mentioned problems is a magnetic base formed of a sintered body that includes sintered particles formed of ferrite containing Ni and Zn, and has a surface layer on the surface in which the ratio of the number of moles of CuO to the total number of moles of copper oxide is 20% or more.

[0010] The present invention also includes, as one aspect, a coil component including the magnetic base, and a circuit board including the coil component. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a magnetic substrate having excellent electrical insulation properties. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram showing a cross-sectional structure of a magnetic substrate according to a first aspect of the present invention; [Figure 2] 1A and 1B are explanatory views of a structural example of a wire-wound coil component among coil components according to a second aspect of the present invention ((a): overall perspective view, (b): AA cross-sectional view in (a)). [Figure 3] 1A and 1B are explanatory views of a structural example of a laminated coil component among coil components according to a second aspect of the present invention ((a): overall perspective view, (b): BB cross-sectional view in (a)). [Figure 4] FIG. 10 is an explanatory diagram showing a method for producing a compact having a conductor precursor disposed therein, for producing a laminated coil component according to a second aspect of the present invention. [Figure 5] Graph showing the relationship between the ratio of Cu2O in copper oxide in the surface layer and the resistivity for magnetic substrates according to examples and comparative examples of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] The configuration and effects of the present invention will be described below, along with the technical concept, with reference to the drawings. However, the mechanism of action includes assumptions, and the correctness of such assumptions does not limit the present invention.

[0014] [Magnetic substrate] A magnetic substrate according to one aspect of the present invention (hereinafter sometimes simply referred to as "first aspect") is formed of a sintered body 10a that includes sintered particles 1 formed of ferrite containing Ni and Zn, and has a surface layer 2 on the surface in which the ratio of the number of moles of Cu2O to the total number of moles of copper oxide is 20% or more, as shown schematically in Figure 1. This sintered body 10a may have an interface layer 3 at the interface between the sintered particles 1.

[0015] The ferrite constituting the sintered particle 1 in the first aspect contains Ni and Zn in addition to Fe as constituent elements, has a spinel-type crystal structure, and is called Ni-Zn ferrite. Furthermore, ferrites containing Cu in addition to the above elements are sometimes called Ni-Zn-Cu ferrites. A typical composition of Ni-Zn ferrite, calculated as Fe2O3, NiO, and ZnO, is 47.3 mol% to 49.8 mol% Fe2O3, 15.0 mol% to 36.9 mol% NiO, and 15.0 mol% to 36.9 mol% ZnO, when the total of these oxides is taken as 100 mol%. A typical composition of Ni-Zn ferrite expressed in mass % is 64.4 to 67.4 mass % Fe2O3, 9.4 to 23.8 mass % NiO, and 10.4 to 25.6 mass % ZnO, calculated as Fe2O3, ZnO, and NiO, when the total of these oxides is taken as 100 mass %. A typical composition of Ni-Zn-Cu ferrite expressed in mass % is 41.6 to 49.3 mol % Fe2O3, 13.3 to 36.5 mol % NiO, 13.3 to 36.5 mol % ZnO, and 1.0 to 12.1 mol % CuO, calculated as Fe2O3, NiO, ZnO, and CuO, when the total of these oxides is taken as 100 mol %. Furthermore, a typical composition of Ni-Zn-Cu ferrite expressed in mass % is, converted into Fe2O3, ZnO, NiO, and CuO, and when the total of these oxides is taken as 100 mass %, 58.9 mass % to 66.9 mass % Fe2O3, 8.6 mass % to 23.6 mass % NiO, 9.5 mass % to 25.4 mass % ZnO, and 0.6 mass % to 8.6 mass % CuO.

[0016] In the Ni-Zn ferrite and Ni-Zn-Cu ferrite described above, increasing the Fe2O3 content improves the relative permeability and saturation magnetic flux density of the magnetic substrate. Furthermore, in these ferrites, the magnitude of the relative permeability of the magnetic substrate varies depending on the NiO to ZnO ratio (NiO / ZnO). Furthermore, in Ni-Zn-Cu ferrite, increasing the CuO content improves the relative permeability of the magnetic substrate. Thus, the ferrite of the first aspect allows the properties of the magnetic substrate to be adjusted by the composition.

[0017] The composition of the ferrite constituting the sintered particle 1 is determined by the following procedure. First, the sintered body 10a is cut or ground to expose a smooth surface not covered with the surface layer 2 described below. Next, carbon is vapor-deposited on the exposed surface to impart conductivity and create a measurement surface. The measurement surface is then observed using a scanning electron microscope (SEM) equipped with either an energy-dispersive X-ray spectrometer (EDS) or a wavelength-dispersive X-ray spectrometer (WDS). The sintered particle 1 is identified as a relatively bright area surrounded by a dark area. The types and amounts of elements contained in an arbitrary location near the center of the sintered particle 1 are then measured and calculated using EDS or WDS. The content ratios of Fe2O3, ZnO, NiO, and CuO are calculated in mol% or mass% from the contents of Fe, Ni, Zn, and Cu. This measurement and calculation is performed for five locations, and the average content ratio of each component is calculated. In a sintered body obtained by a general manufacturing method, the content ratio of each element near the center of the sintered particle 1 is constant regardless of position, and there is usually no significant difference in the content ratio of each element between different sintered particles 1, so in this case the measurement points may be multiple points within one sintered particle 1, or one point may be selected from each different sintered particle 1. Finally, each calculated average value is divided by the sum of the average values ​​and then multiplied by 100 to calculate the content ratio of each oxide when the sum of the oxides is 100%, and this is the composition of the ferrite.

[0018] A surface layer 2 is present on the surface of the sintered body 10a. This surface layer 2 is distinguishable from the sintered particles 1 by differences in composition or atomic or ionic arrangement. For example, when a cross section of the sintered body 10a is analyzed by the above-mentioned EDS or WDS to map the distribution of elements, the element concentration at the periphery of the cross section differs from that of the sintered particles 1; when the periphery of the cross section of the sintered body 10a is observed with a transmission electron microscope (TEM), a structure different from that of the sintered particles 1 is confirmed; and when X-ray diffraction (XRD) is measured on the surface of the sintered body 10a, a diffraction line different from that derived from a spinel-type crystal structure is observed as the strongest line. All of these can be said to support the presence of the surface layer 2.

[0019] In this surface layer 2, the ratio of the number of moles of Cu2O to the total number of moles of copper oxide is 20% or more.

[0020] The sintered body 10a has a high resistivity due to the presence of the surface layer 2, and the electrical insulation of the magnetic substrate formed from the sintered body is improved. The reason for this is not clear, but it is thought to be due to the following mechanism of action.

[0021] CuO and CuO are known as copper oxides contained in the surface layer 2, and CuO is considered to have a higher resistivity than CuO. For this reason, it is presumed that the surface layer 2 containing a certain proportion or more of CuO as copper oxide has a significantly higher resistivity, and the resistivity of the sintered body 10a including the surface layer 2 increases.

[0022] In order to obtain a higher resistivity for the sintered body 1, the ratio of the number of moles of Cu2O to the total number of moles of copper oxide in the surface layer 2 is preferably 30% or more, more preferably 50% or more, and even more preferably 70% or more.

[0023] The proportion of Cu2O in the copper oxide in the surface layer 2 is calculated using the following procedure. First, the surface of the sintered compact 10a having the surface layer 2 is measured and analyzed by Auger electron spectroscopy (AES). The measurement is performed by point analysis of any location on the sample surface under conditions of an acceleration voltage of 3 kV, a probe current of 5 nA, and a sample tilt of 75 degrees. Next, qualitative analysis of various elements is performed on the measurement results to confirm the presence of Cu. Next, a state analysis of Cu is performed, and the proportions of Cu2O and CuO are calculated in mol%. Next, from the calculated proportions of Cu2O and CuO, the ratio of the proportion of Cu2O to the total is calculated.

[0024] The surface layer 2 preferably covers the entire surface of the sintered body 10a. However, even if there are portions where the sintered particles 1 are exposed, as long as the proportion of the area of ​​the exposed portions to the total surface area of ​​the sintered body 10a is relatively small and the exposed portions are not concentrated in specific locations on the sintered body 10a, a magnetic base having the desired electrical insulation properties can be obtained.

[0025] The sintered body 10a may have an interface layer 3 at the interface between the sintered particles 1, which has a higher Cu content than the sintered particles. This allows for a magnetic substrate with excellent stress characteristics. This is presumably because the interface layer 3, which is rich in Cu and has a different atomic or ionic arrangement from the sintered particles 1, functions as a stress relaxation layer, thereby reducing the stress applied to the sintered particles 1.

[0026] The presence of the interface layer 3 in the sintered body 10a can be confirmed by the following procedure. First, a measurement surface is formed and observed under an SEM in the same manner as in the above-described method for determining the ferrite composition. An SEM image of the measurement surface is obtained to determine the positions of the sintered particles 1 and their interfaces. Next, the Cu distribution is measured using EDS or WDS in the SEM-observed region, and a mapping image is obtained. Finally, the SEM image and the mapping image are compared, and if a high Cu concentration area in the mapping image overlaps with the interface of the sintered particles 1 in the SEM image, the overlapping area is determined to be the interface layer 3. As described below, the interface layer 3 is formed by the separation of Cu from the particles constituting the calcined powder during sintering. Therefore, the majority of the constituent elements are Cu, and the proportion of Cu is significantly higher than that of the sintered particles 1. Therefore, the high Cu concentration area in the mapping image can be easily distinguished from other areas.

[0027] In the first aspect, the sintered body is allowed to contain unavoidable impurities up to several hundred ppm, such as typical elements B, C, S, Cl, Se, Br, Te, I, Li, Na, Mg, Al, K, Ga, Ge, Sr, In, Sn, Sb, Ba, Pb, and Bi, as well as transition elements Sc, Ti, V, Cr, Y, Nb, Mo, Pd, Ag, Cd, Hf, and Ta.

[0028] In the first aspect, various subcomponents may be added in addition to the essential components described above to obtain a magnetic substrate with better magnetic properties within a range that allows the desired electrical insulation to be achieved.

[0029] [Method for manufacturing magnetic substrate] The magnetic substrate according to the first aspect can be manufactured by the following steps: preparing raw material powder containing Fe, Ni, Zn, and Cu; blending and mixing the raw material powder so that the elements are contained in a desired ratio to prepare a mixed powder; heat-treating the mixed powder to prepare a calcined powder mainly composed of ferrite having a spinel structure; molding the calcined powder into a compact; and heat-treating the compact by increasing the temperature at a rate of 500°C / h or more through a temperature range of 500°C to 750°C, heating it to a temperature of 800°C to 1100°C, and then cooling it at a rate of 500°C / h or more through a temperature range of 750°C to 500°C, in an oxygen-containing atmosphere having an oxygen concentration equal to or lower than that in air.

[0030] The raw material powder used is not particularly limited as long as it contains Fe, Ni, Zn, and Cu, and various compounds, including elemental metals, alloys, and oxides, can be used. Compounds may also be those containing multiple types of the aforementioned elements, such as composite oxides. Among these, the oxides Fe2O3, NiO, ZnO, and CuO are preferred because they have little variation in particle shape and particle size, and powders consisting of small particles are readily available.

[0031] The particle size of the raw material powder to be used is not particularly limited, and may be, for example, an average particle size (median diameter (D 50 )) can be set to 0.1 μm or more and 5 μm or less. The average particle size is preferably 0.5 μm or more and 3.5 μm or less, more preferably 0.5 μm or more and 2.5 μm or less, and even more preferably 0.5 μm or more and 1.5 μm or less. When the average particle size is equal to or more than the lower limit, handling becomes easy. On the other hand, when the average particle size is equal to or less than the upper limit, the synthesized ferrite tends to be uniform. This average particle size can be measured, for example, using a particle size distribution measuring device using a laser diffraction / scattering method.

[0032] The blending amounts of the raw material powders should be such that ferrite of the desired composition is produced. When determining the blending amounts, it is advisable to confirm through preliminary experiments that a sintered body of the desired composition and structure can be obtained, taking into consideration that Cu can contribute to the formation of ferrite, the surface layer, and the interface layer, and that the contribution rate of Cu to the formation of these three layers can vary depending on the conditions of the heat treatment of the compact, as described below. Examples of blending amounts when Fe2O3, NiO, ZnO, and CuO are used as raw material powders include Fe2O3 at 47 mol% to 50 mol%, NiO at 14 mol% to 32 mol%, ZnO at 17 mol% to 30 mol%, and CuO at 3 mol% to 12 mol%.

[0033] The method for blending and mixing the raw material powders is not particularly limited as long as the powders are mixed uniformly while preventing the mixing of impurities, and either dry mixing or wet mixing may be used. When wet mixing using a ball mill is used, the mixing time can be, for example, from 8 hours to 24 hours.

[0034] The heat treatment conditions for obtaining the calcined powder from the mixed powder are not limited as long as the raw materials react to produce Ni-Zn ferrite or Ni-Zn-Cu ferrite having the desired composition, and may be, for example, in an air atmosphere at 500°C to 1000°C for 1 hour to 2 hours. When determining the heat treatment conditions, it is advisable to consider the following: a low temperature or a short time may result in unreacted raw materials or intermediate products remaining; a high temperature or a long time may result in the evaporation of components, making it impossible to obtain a compound with the desired composition, or the product may solidify and become difficult to disintegrate, resulting in reduced productivity.

[0035] If the calcined powder obtained by the heat treatment described above is agglomerated, it is preferable to pulverize it before molding. The pulverization is carried out to break down the agglomerations of the calcined powder and obtain a powder with appropriate sinterability. The pulverization may be carried out in a dry manner using a vibration mill, hammer mill, roller mill, or the like, but when the calcined powder forms large lumps, it is preferable to carry out the pulverization in a wet manner using a ball mill, attritor, or the like after coarse pulverization. The pulverization is carried out until the average particle size of the calcined powder is 0.5 μm or more and 2 μm or less, or until the BET specific surface area of ​​the calcined powder is 2.0 m 2 / g or more 3.0m 2 It is preferable to perform the process until the sintering temperature reaches 1 / g or less in terms of moldability, shape retention, and sinterability.

[0036] Furthermore, prior to molding the calcined powder, the calcined powder may be granulated to obtain a granulated product (granules). Granulation is carried out to convert the pulverized material into agglomerated particles of an appropriate size and convert them into a form suitable for molding. Examples of such granulation methods include pressurized granulation and spray drying.

[0037] Furthermore, prior to molding the calcined powder, a binder may be mixed with the calcined powder to improve shape retention after molding. The binder used is preferably one that can bond the particles of the calcined powder together to enable molding and shape retention, and that decomposes and volatilizes at temperatures of 500°C or less. Examples of such binders include acrylic resin, butyral resin, and vinyl resin. The amount of binder added can be determined appropriately taking into account moldability, shape retention, and the like, and can be, for example, 0.1 to 5 parts by mass per 100 parts by mass of the calcined powder. An example of a method for mixing the calcined powder and binder is mixing using a ball mill.

[0038] The method for molding the calcined powder or a mixture thereof with a resin is not particularly limited, and for example, a method in which the powder or the mixture is supplied to a molding die such as a metal mold and pressed with a press or the like to form the powder or the mixture is applicable. Alternatively, a method in which green sheets containing the calcined powder and a resin are laminated and pressed together may also be applied. The shape of the molded body is also not particularly limited, and may be appropriately selected from known shapes such as a rod, plate, toroidal, or drum shape depending on the application.

[0039] When a compact is obtained by press molding using a mold or the like, the pressing conditions may be determined appropriately depending on the type of calcined powder and the resin to be mixed therewith, the blending ratio thereof, etc. An example of the pressing pressure is 5 ton / cm. 2 More than 10ton / cm 2 The following can be cited: When the pressing pressure is equal to or greater than the lower limit, a compact with a high filling rate can be obtained. On the other hand, when the pressing pressure is equal to or less than the upper limit, destruction of the particles constituting the calcined powder is suppressed, and variation in particle size of the sintered particles in the obtained sintered body is suppressed.

[0040] When green sheets are laminated and pressed to obtain a molded body, a method can be adopted in which individual green sheets are stacked using a suction conveyor or the like and then thermocompressed using a press. When multiple coil components are to be obtained from the pressed laminate, the laminate may be divided using a cutting machine such as a dicing machine or a laser cutting machine.

[0041] In this case, the green sheet is typically produced by applying a slurry containing the calcined powder and a binder to the surface of a base film such as a plastic film using a coating machine such as a doctor blade or a die coater, followed by drying. Examples of binders suitable for producing the green sheet include polyvinyl acetal resins such as polyvinyl butyral. Furthermore, the solvent for preparing the slurry may be, but is not limited to, glycol ethers such as butyl carbitol. The content of each component in the slurry may be appropriately adjusted depending on the green sheet forming method used, the thickness of the green sheet to be produced, and other factors.

[0042] If the compact obtained by compacting contains a binder, a degreasing treatment is performed to remove the binder prior to firing. In the degreasing treatment, the compact is heated in the presence of oxygen to volatilize the binder through oxidation. The conditions for the degreasing treatment are not particularly limited as long as they can oxidize and remove most of the binder without sintering the calcined powder particles in the compact. One example is holding the compact in air at a temperature of 300°C to 450°C for 2 hours to 4 hours.

[0043] The heat treatment of the compact obtained by molding and degreasing as necessary is carried out under conditions in which the temperature is increased at a rate of 500°C / h or more in the temperature range from 500°C to 750°C, heated to a temperature of 800°C to 1100°C, and then decreased at a rate of 500°C / h or more in the temperature range from 750°C to 500°C. This results in a sintered body having a surface layer containing copper oxide, where the ratio of the number of moles of CuO to the total number of moles of copper oxide is 20% or more, and an interface layer at the interface between the sintered particles, which has a higher Cu content than the sintered particles.

[0044] The reason why the surface layer and the interface layer are formed by heat treatment under the above-mentioned conditions is unclear, but it is thought to be due to the following mechanism. During the sintering process of Ni-Zn-Cu ferrite, depending on the composition of the calcined powder and the heat treatment conditions, Cu, which contributes to improving sinterability, may remain on the surface of the sintered particles. Under conventional heat treatment conditions, this remaining Cu is presumably bonded with a sufficient amount of oxygen in the temperature range from 500°C to 750°C, resulting in the majority of CuO. On the other hand, under the above-mentioned heat treatment conditions, where the time spent in this temperature range is significantly shortened, the remaining Cu is presumably unable to bond with a sufficient amount of oxygen, resulting in the formation of a large amount of CuO, which has a lower oxygen-to-Cu ratio than CuO. In particular, the surface of the sintered body is presumably more sensitive to temperature changes in the heat treatment equipment (heat source), resulting in a shorter time spent in this temperature range than the interior of the sintered body, resulting in a higher proportion of CuO in the surface layer formed by the remaining Cu.

[0045] In the heat treatment of the compact, the heating and cooling rates in the temperature range from 500°C to 750°C are preferably 600°C / h or higher, and more preferably 700°C / h or higher. Increasing the heating and cooling rates in this temperature range increases the ratio of CuO moles to the total moles of copper oxide in the surface layer of the sintered body, thereby improving resistivity. It also moderately suppresses the growth of sintered particles, improving the stress characteristics of the magnetic substrate. While there is no upper limit to the heating and cooling rates in this temperature range, taking into account the performance of the heat treatment device, it is approximately 1200°C / h. That is, the heating and cooling rates in this temperature range are typically 500°C / h to 1200°C / h, preferably 600°C / h to 1200°C / h, and more preferably 700°C / h to 1200°C / h. In the past, it was thought that if the heating and cooling rates were increased when sintering Ni-Zn ferrite or Ni-Zn-Cu ferrite, a difference in shrinkage would occur between the surface and the interior of the compact or sintered body, resulting in a problem of increased internal stress in the resulting sintered body. For this reason, the heating and cooling rates during heat treatment were usually set low.

[0046] The heat treatment of the compact is carried out in an oxygen-containing atmosphere having an oxygen concentration equal to or lower than that in air. Of course, the oxygen-containing atmosphere may be air. To increase the ratio of the number of moles of CuO to the total number of moles of copper oxide in the surface layer, the oxygen concentration in the oxygen-containing atmosphere is preferably 10,000 ppm (1%) or less, more preferably 5,000 ppm or less, and even more preferably 3,000 ppm or less. On the other hand, to maintain the properties of ferrite, which is an oxide, the oxygen concentration in the oxygen-containing atmosphere is preferably 100 ppm or more, more preferably 300 ppm or more, and even more preferably 500 ppm or more. That is, the oxygen concentration in the oxygen-containing atmosphere during the heat treatment is preferably 100 ppm or more and 10,000 ppm or less (1%), more preferably 300 ppm or more and 5,000 ppm or less, and even more preferably 500 ppm or more and 3,000 ppm or less.

[0047] In the heat treatment of the compact, the temperature may be raised to over 750°C and then held at a specific temperature for a predetermined time. This further promotes sintering, resulting in a dense sintered body. One example of the holding mode is holding at the heating temperature (maximum temperature reached) for 30 minutes to 2 hours.

[0048] The above-mentioned degreasing treatment and heat treatment may be carried out continuously using a single heat treatment device capable of changing the atmosphere and temperature settings, or may be carried out intermittently using two or more different heat treatment devices.

[0049] [Coil parts] A coil component 100 according to a second aspect of the present invention (hereinafter, sometimes simply referred to as the "second aspect") comprises a magnetic base 10 according to the first aspect described above, and a conductor 20 arranged inside or on the surface of the magnetic base 10, as illustrated in Figures 2 and 3.

[0050] The material, shape, and arrangement of the conductor 20 are not particularly limited and may be determined appropriately depending on the required characteristics. Examples of materials include silver, copper, or alloys thereof. Examples of shapes include linear, meander, planar coil, and spiral. Examples of arrangements include a coated conductive wire as the conductor 20 wound around the magnetic substrate 10, or various shapes of conductors 20 embedded inside the magnetic substrate 10.

[0051] Examples of the shape and structure of the second side surface include a wound coil component as shown in FIG. 2 and a laminated coil component as shown in FIG.

[0052] The second aspect is that the coil component has low loss because the magnetic base 10 has high resistivity and excellent electrical insulation, thereby suppressing the amount of current flowing through the magnetic base 10.

[0053] [Coil component manufacturing method 1] The coil component according to the second aspect described above can be manufactured by disposing a conductor on the surface of the magnetic base according to the first aspect. Specific examples of the disposing method include a method of winding a coated conductive wire around the magnetic base, and a method of disposing a conductor precursor on the surface of the magnetic base by printing a conductor paste or the like, and then performing a baking process using a heating device such as a baking furnace.

[0054] [Coil component manufacturing method 2] Furthermore, the coil component according to the second aspect can also be manufactured by simultaneously forming the magnetic base and the conductor according to the first aspect, through the steps of preparing raw material powder containing Fe, Ni, Zn, and Cu, blending and mixing the raw material powder to prepare a mixed powder so that the elements are contained in a desired ratio, heat-treating the mixed powder to prepare a calcined powder mainly composed of ferrite having a spinel structure, mixing the calcined powder with a resin to obtain a mixture, molding the mixture and a precursor of a conductor to form a compact having the precursor disposed therein, degreasing the compact, and subjecting the degreasing-treated compact to a heat treatment in an oxygen-containing atmosphere having an oxygen concentration equal to or lower than that in air, in which the magnetic base and the conductor according to the first aspect are simultaneously formed.

[0055] In this case, the method for preparing the calcined powder and the type and amount of binder mixed with the calcined powder are the same as those used in the manufacture of the magnetic base according to the first aspect described above, and therefore a description thereof will be omitted.

[0056] As shown in Fig. 4, the molded body having a conductor precursor disposed therein is obtained by processing via holes 32 in a green sheet 31 used for manufacturing the magnetic substrate according to the first aspect described above, disposing conductor precursors 33 on the green sheet 31 by printing a conductor paste or the like, and laminating and pressing a plurality of green sheets 31. Here, the conductor precursor 33 means a material that contains a binder resin and the like in addition to a conductive material that forms a conductor in a coil component, and becomes a conductor by heat treatment.

[0057] The conductive paste used may contain a conductive powder and an organic vehicle. The conductive powder may be a powder of silver, copper, or an alloy thereof. The particle size of the conductive powder is not particularly limited, but for example, a powder with an average particle size (median diameter (D50)) of 1 μm to 10 μm calculated from the particle size distribution measured on a volume basis may be used. The composition of the organic vehicle may be determined taking into consideration its compatibility with the binder contained in the green sheet. One example is a polyvinyl acetal resin such as polyvinyl butyral (PVB) dissolved or swollen in a glycol ether solvent such as butyl carbitol. The blending ratio of the conductive powder and the organic vehicle in the conductive paste can be adjusted appropriately depending on the viscosity of the paste suitable for the printing machine used and the film thickness of the conductive pattern to be formed.

[0058] The conditions for the degreasing treatment performed on the compact containing the conductor precursor disposed therein are the same as those for manufacturing the magnetic base according to the first aspect described above, and therefore a detailed description thereof will be omitted. Furthermore, the conditions for the heat treatment performed after the degreasing treatment are also the same as those described above, except that the heating temperature (maximum temperature reached) is slightly lower, at 800°C or higher and 950°C or lower, and therefore a detailed description thereof will be omitted. The heating temperature for the heat treatment is set low in order to prevent the generated conductor from melting.

[0059] [Circuit board] A circuit board according to a third aspect of the present invention (hereinafter, may be simply referred to as the "third aspect") is a circuit board on which the coil component according to the second aspect described above is mounted.

[0060] The structure of the circuit board is not limited, and any structure may be adopted depending on the purpose.

[0061] The third side face has a small loss due to the use of the coil component related to the second side face. [Example]

[0062] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0063] [Example 1] <Magnetic body and coil component manufacturing> First, Fe2O3, NiO, ZnO, and CuO were prepared as raw material powders. Next, these raw material powders were weighed so that Fe2O3 was 49 mol%, NiO was 28 mol%, and ZnO was 23 mol%, and the ratio of CuO to the total of Fe2O3, NiO, and ZnO was 8 mass%, and mixed in a wet ball mill. Next, the dispersion medium was evaporated and removed, and the obtained mixed powder was heat-treated in an air atmosphere at 900 °C for 2 hours to obtain a calcined powder. Next, the obtained calcined powder was mixed with a sintered powder having a BET specific surface area of ​​3.0 m 2 The powder was crushed to a mass of 10 ... Through this heat treatment, a disk-shaped magnetic substrate having a diameter of 8 mm and a thickness of 0.5 mm, a toroidal-shaped magnetic substrate having an outer diameter of 25 mm, an inner diameter of 12 mm, and a thickness of 15 mm, and a square plate-shaped magnetic substrate having a thickness of 3 mm and a 15 mm square with a 5 mm square hole in the center were obtained. Finally, a conducting wire was wound 20 turns around one side of the obtained square plate-shaped magnetic substrate, i.e., the portion sandwiched between the side forming the central hole and the side forming the outer periphery, to obtain a test coil component according to Example 1.

[0064] <Surface layer analysis of magnetic substrate (sintered body)> The proportion of CuO in the copper oxide in the surface layer of the obtained toroidal-shaped magnetic substrate was calculated using the method described above. A field emission scanning electron microscope (FE-SEM) equipped with EDS (MERLIN, manufactured by Carl Zeiss) was used to measure the content of each element in the surface layer, and a field emission Auger microprobe (JAMP-9510F, manufactured by JEOL Ltd.) was used for Auger electron spectroscopy (AES) analysis. As a result, the molar proportion of CuO in the copper oxide was calculated to be 25%.

[0065] <Confirmation of the interface layer in the magnetic material (sintered body)> The presence or absence of an interface layer in the sintered body of the obtained toroidal-shaped magnetic substrate was confirmed using the method described above. FE-SEM (MERLIN, manufactured by Carl Zeiss) equipped with EDS was used to obtain SEM images and mapping images. As a result, it was determined that the sintered body had an interface layer inside.

[0066] <Measurement of resistivity of magnetic materials (sintered materials)> Ag paste was applied to the front and back surfaces of the obtained disk-shaped magnetic substrate (the two opposing surfaces with the largest area) and then baked to form electrodes. Next, the electrical resistance value of this test magnetic substrate was measured using a resistance meter (manufactured by Hioki E.E. Corporation, RM3544), and the specific resistance was calculated from the obtained electrical resistance value, the electrode area, and the thickness of the test magnetic substrate. The obtained specific resistance was 4 × 10 8 The resistance was Ω·cm.

[0067] <Measurement of stress characteristics of magnetic materials (sintered materials)> For the obtained test coil component, the relative permeability μ0 was measured at room temperature under conditions of an OSC level of 500 mV and a frequency of 1 MHz using an impedance analyzer (Keysight Technologies, Inc., 4294A) without applying stress. The relative permeability μ1 was also measured under the same conditions, except that a compressive load of 30 kgf was applied to the side of the test coil component facing the winding (non-winding portion) using a pressure machine. From these measurement results, the stress characteristic was calculated as (μ1 - μ0) / μ0 × 100 (%), which was -3%.

[0068] [Example 2] The magnetic substrate and test coil components of Example 2 were produced using the same procedure as in Example 1, except that the temperature conditions for the heat treatment were such that the temperature was increased from 500°C to 900°C at a rate of 500°C / h, held at 900°C for 1 hour, and then decreased from 900°C to 500°C at a rate of 500°C / h.

[0069] For the obtained magnetic substrate and test coil component, the proportion of CuO in the copper oxide in the surface layer was calculated, the presence or absence of an interface layer was confirmed, and the resistivity and stress characteristics were measured and calculated in the same manner as in Example 1. As a result, the proportion of the number of moles of CuO in the copper oxide in the surface layer was calculated to be 23%, and it was determined that the sintered body constituting the magnetic substrate had an interface layer inside, and the resistivity of the magnetic substrate was 3×10 8 The calculated values ​​of Ω·cm and stress characteristics were -3%, respectively.

[0070] [Examples 3 to 5] A magnetic base and coil component according to Example 3 were produced using the same procedure as in Example 1, except that the atmosphere in which the heat treatment was performed was a nitrogen-oxygen mixed gas with an oxygen concentration of 10,000 ppm. A magnetic base and coil component according to Example 4 were produced using the same procedure as in Example 1, except that the atmosphere in which the heat treatment was performed was a nitrogen-oxygen mixed gas with an oxygen concentration of 3,000 ppm. A magnetic base and test coil component according to Example 5 were produced using the same procedure as in Example 1, except that the atmosphere in which the heat treatment was performed was a nitrogen-oxygen mixed gas with an oxygen concentration of 500 ppm.

[0071] For the obtained magnetic substrates and test coil components, the proportion of Cu2O in the copper oxide in the surface layer was calculated, the presence or absence of an interface layer was confirmed, and the resistivity and stress characteristics were measured and calculated using the same methods as in Example 1. As a result, in the magnetic substrates according to all Examples, it was determined that the sintered body constituting the magnetic substrate had an interface layer inside. Furthermore, the proportion of the number of moles of Cu2O in the copper oxide in the surface layer was calculated to be 30% in Example 3, 52% in Example 4, and 76% in Example 5. Furthermore, the resistivity of the magnetic substrate was 5 x 10 8 Ω·cm, and in Example 4, 7×10 8 Ω cm, and in Example 5, 11 × 10 8 Ω·cm. Furthermore, the stress characteristics were calculated to be -3% for the magnetic substrates according to all of the examples.

[0072] [Comparative Examples 1 and 2] A magnetic base and coil components according to Comparative Example 1 were produced using the same procedure as in Example 1, except that the temperature conditions for the heat treatment were such that the temperature was increased from 500°C to 900°C at a rate of 350°C / h, held at 900°C for 1 hour, and then decreased from 900°C to 500°C at a rate of 350°C / h. Furthermore, a magnetic base and test coil components according to Comparative Example 2 were produced using the same procedure as in Comparative Example 1, except that the holding time at 900°C was set to 3 hours.

[0073] For the obtained magnetic substrates and test coil components, the proportion of Cu2O in the copper oxide in the surface layer was calculated, the presence or absence of an interface layer was confirmed, and the resistivity and stress characteristics were measured and calculated in the same manner as in Example 1. As a result, in the magnetic substrates according to all Examples, it was determined that the sintered body constituting the magnetic substrate had an interface layer inside. Furthermore, the proportion of the number of moles of Cu2O in the copper oxide in the surface layer was calculated to be 18% in Comparative Example 1 and 17% in Comparative Example 2. Furthermore, the resistivity of the magnetic substrate was 1×10 8 Ω·cm, and in Comparative Example 2 it was 0.8×10 8 Furthermore, the stress characteristics were calculated to be -7% in Comparative Example 1 and -8% in Comparative Example 2.

[0074] Comparative Example 3 A magnetic substrate and test coil component according to Comparative Example 3 were produced using the same procedure as in Example 1, except that the raw material powder was blended so that the proportion of CuO was 3 mass% relative to the total of Fe2O3, NiO, and ZnO.

[0075] For the obtained magnetic substrate, an attempt was made to calculate the proportion of CuO in the copper oxide in the surface layer using the same method as in Example 1. However, qualitative analysis did not confirm any significant content that could be considered the main component of Cu, nor was the presence of CuO confirmed. Furthermore, when the obtained magnetic substrate was checked for the presence or absence of an interface layer using the same method as in Example 1, the presence of an interface layer was not confirmed. When the composition of the outer periphery of the measurement surface where the presence or absence of the interface layer was confirmed was analyzed, no areas with different element concentrations from the sintered particles were found. From this result and the above-mentioned analysis results of the magnetic substrate surface, it is determined that the magnetic substrate according to Comparative Example 3 does not have a surface layer, and the sintered particles are exposed on the surface.

[0076] The resistivity of the test magnetic substrate according to Comparative Example 3 was measured in the same manner as in Example 1. 8 Furthermore, when the stress characteristics of the magnetic substrate of the test coil component according to Comparative Example 3 were measured, the result was -12%.

[0077] The manufacturing conditions for the examples and comparative examples described above are summarized in Table 1, and the results obtained are summarized in Table 2. The relationship between the mole ratio of CuO in the copper oxide in the surface layer and the resistivity is shown in Figure 4.

[0078] [Table 1]

[0079] [Table 2]

[0080] Table 2 and Figure 5 show that magnetic substrates made of sintered bodies having a surface layer containing copper oxide and in which the mole ratio of CuO in the copper oxide is 20% or more have significantly high resistivity, and that these magnetic substrates also have excellent stress characteristics. [Industrial Applicability]

[0081] According to the present invention, a magnetic substrate having excellent electrical insulation properties can be provided. Therefore, the present invention is useful in that low-loss coil components can be obtained. Furthermore, according to a preferred embodiment of the present invention, a magnetic substrate can be provided in which the decrease in magnetic permeability is small even when stress is applied. Therefore, the present invention is also useful in that coil components with small decrease in inductance can be obtained even when stress is applied to the magnetic substrate due to coating with resin or the like. [Explanation of symbols]

[0082] 100 Coil parts 10 Magnetic substrate 10a Sintered body 1. Sintered particles 2 Surface layer 3 Interface layer 20 Conductors 31 Green Sheet 32 Via Hall 33 Conductor precursors

Claims

1. A magnetic substrate used in a coil component, comprising: The sintered particles are formed of ferrite containing Ni and Zn, When the surface was measured and analyzed by Auger electron spectroscopy (AES), the ratio of Cu to the total moles of copper oxide was ２ The sintered body has a surface layer in which the ratio of the number of moles of O is 20% or more, the surface layer covers the surfaces of the sintered particles on the surface of the sintered body, thereby covering at least a portion of the surface of the sintered body; The magnetic substrate has a composition of the sintered particles in which, when the total of Fe2O3, NiO, ZnO, and CuO is 100 mol%, Fe2O3 is 41.6 mol% or more and 49.3 mol% or less, NiO is 13.3 mol% or more and 36.5 mol% or less, ZnO is 13.3 mol% or more and 36.5 mol% or less, and CuO is 1.0 mol% or more and 12.1 mol% or less.

2. 2. The magnetic substrate according to claim 1, wherein an interface layer having a higher Cu content than the sintered particles is formed at the interface between the sintered particles.

3. A magnetic substrate as described in claim 1 or 2, wherein the surface layer covers the entire surface of the sintered body.

4. A coil component comprising: the magnetic substrate according to claim 1; and a conductor disposed inside the magnetic substrate.

5. A coil component comprising: the magnetic substrate according to claim 1; and a coated conductor wound around the magnetic substrate.

6. A circuit board on which the coil component according to claim 4 or 5 is mounted.

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